The present invention relates to an improved washing process to be carried out in an automatic dishwashing machine.
As is known, automatic dishwashing machines are provided with an electromechanical or electronic program control device arranged to control the main operative devices of the machine by carrying out different predetermined programs which can be selected by the user.
A modern dishwashing machine, for example, is capable of performing operative processes consisting of one or more successive phases which are selectively included in, or excluded from each program. More particularly, a program may effect a prewashing phase in which the articles are washed with washing solution at ambient temperature and/or a prewashing phase with heated washing solution, an actual washing phase, a rinsing phase in which the articles so washed are rinsed with water at ambient temperature and/or with heated water, a drying phase, etc.
The program which effects an actual washing phase, or so-called "wash cycle", is particularly important, particularly in light of the current trends of providing energy savings. As is known, a wash cycle is carried out by supplying a volume of water (usually at ambient temperature) into the wash tub of the machine, adding a metered amount of detergent (which is commonly a powdered detergent including a surfactant) to the water to form a washing solution, heating the so formed washing solution, and subjecting the articles to be washed, which are exposed to the washing solution, to a mechanical action. In a dishwasher, in particular, the articles to be washed are sprayed with the washing solution by means of special rotary spray arms, or the like.
During the progression of the washing operation, the detergent solubilizes the dirt (the organic fatty substances, for example) on the articles being washing and forms an emulsion thereof in the washing solution which at least in part tends to deposit on the bottom of the wash tub. After a given time period, therefore, the detergent exerts its chemical action not only on the dirt which is still to be removed from the articles, but also on the dirt which has already been removed therefrom and is suspended in the washing solution or has been deposited on the bottom of the wash tub. More particularly, part of the dirt released from the articles is deposited on the portion of the drain circuit at the bottom of the dishwasher along with a corresponding amount of detergent which is thus unused.
In any case, after a certain time period from the beginning of the washing process, the chemical action exerted by the detergent is partially wasted in attacking the amount of dirt which has already been removed from the articles being washed.
As has already been stated, in some known operative programs the washing phase is preceded by a prewashing phase carried out with heated washing solution in order to obtain a more effective result. Mainly, the prewashing phase has the function of mechanically removing coarse dirt particles from the articles being washed, thereby promoting the effectiveness of the subsequent actual washing phase. To this aim, the prewashing phase terminates with a drain step in which the washing solution is completely discharged, thereby discharging the dirt formerly removed; obviously, this reduces the above-mentioned problem of partially wasting the detergent used during the subsequent washing phase.
However, the subsequent washing phase is carried out as described above, by using a further volume of water to which a further amount of detergent is added and which has to be completely heated up. Therefore, the entire process has an undesirably long duration and generally involves a remarkable consumption of water and detergent, as well as a corresponding consumption of energy. Of course, this is in contrast with the current needs to save energy.
FR-A-2 128 575 teaches a washing process for clothes washing machines including a washing phase in which the washing solution is first heated up to a predetermined temperature and is eventually partially discharged. After the initial washing phase, an additional subsequent washing phase is performed by adding a further amount of fresh water and a further amount of detergent to the remaining washing solution, which is again heated up to the predetermined temperature. The additional washing phase replaces a traditional bleaching phase using corrosive bleaching agents, but undesirably prolongs the entire washing process and requires a substantial amount of detergent and energy. At any rate, no bleaching phase is commonly carried out in a dishwashing machine.